Security systems in general require the entry of a predetermined digital pass or access code in order to disarm the system so that authorized users of the system may operate freely within a protected area. The protected area may be a plant, residence or even a location within a building. These protected areas are commonly protected by two generically different types of systems. The first type of system is usually enabled 24 hours a day and can include fire detection or detection of an emergency situation which, for instance, could be the actuation of a hold-up switch, the occurrence of a medical emergency, or the actuation of a "panic button" to indicate an unspecified emergency. Other types of continuously monitored systems include tamper detection or facility monitoring including the transmission of data such as building temperature, boiler pressure, etc., for recording and analysis.
Other types of protection provided by security systems include those which are actuated on a periodic basis, for instance, at night or when personnel leave a protected facility. This type of detection includes volumetric protection in which motion sensors of the ultrasonic, passive infrared, or microwave variety detect motion within a given area. Other types of systems which are actuated on a periodic basis are perimeter detection systems and more particularly point detection systems in which for instance door contacts are utilized to detect the intrusion into a building through the door. Vibration detectors detect, for instance, footsteps or the use of saws and acetylene torches, whereas glass break detectors detect the intrusion via the breaking of glass. Moreover, for safes, capacitive proximity detectors are utilized. It is a feature of these latter types of protection that they are to be disarmed during off hours by maintenance personnel, and service personnel or others who need access to the facility. It is, however, desirable that such personnel not be given overall access to the system to avoid compromising the entire system. More specifically, it is highly detrimental to give out a single pass code to everyone needing access to a building because this may permit resetting of the system, enable a user to by-pass selected protection loops, or permit a user to reprogram the system. Such a situation is equivalent to giving out a master key that provides unlimited access to a facility. In short, a single pass code cannot provide for different levels of access. Thus, a single pass code system cannot distinguish between the duties of a general manager and those of a janitor. It is therefore convenient that a system be made to operate with codes which may be assigned as frequently as on a daily basis so as to provide only limited access for certain levels of personnel.
For residential applications, it is also sometimes desirable to permit persons access to a house for a limited period of time as for a vacation without revealing a permanent pass code which would enable entry at an other than authorized time. Providing a permanent pass code would, in effect, be giving an individual a master key which could be utilized at any time.
Thus, the security systems which utilize a single pass code suffer from the inability to establish various levels of access to the facility. Moreover, when a single pass code is used, it is not conveniently changed for temporary access situations, primarily due to problems in notifying all users of the system.